Control system, and control method

ABSTRACT

This control system is provided with a plurality of slave devices and controllers. The controller is connected to one end of a field bus which includes the plurality of slave devices that is linearly connected, and the controller is connected to the other end of the field bus through a communication cable. The controllers are provided with a CPU and a transception part. One of the controllers generates a control frame with the CPU and transmits this from the transception part, and the other of the controllers performs a loop communication of the control frame by the transception part.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 application of the International PCTapplication serial no. PCT/JP2018/025185, filed on Jul. 3, 2018, whichclaims the priority benefit of Japan Patent Application No. 2017-133765,filed on Jul. 7, 2017. The entirety of each of the above-mentionedpatent applications is hereby incorporated by reference herein and madea part of this specification.

TECHNICAL FIELD

The present invention relates to a control system including a controllerand a slave device.

BACKGROUND ART

At present, many factory automation (FA) systems are in practical use.An FA system includes a controller and a plurality of slave devices. Theplurality of slave devices includes a measuring instrument, a switch, acontrol driver and the like, and control target equipment is connectedto the control driver. The controller transmits control data to theplurality of slave devices. In addition, the controller receivesmeasurement data and the like from the plurality of slave devices togenerate control data in the next control cycle.

The controller and the plurality of slave devices are connected to eachother through, for example, a communication cable or the like asdisclosed in Patent Literature 1 (Japanese Patent Application Laid-OpenNo. 2011-35664), and communicate the above-described data according to anetwork standard of Ethernet (registered trademark) or EtherCAT(registered trademark).

SUMMARY OF INVENTION

However, in a configuration of the related art, control for a pluralityof slave devices is stopped when a controller fails. In addition, whenfirmware of the controller is rewritten, or the like, the controller istemporarily stopped. Also in this case, control for a plurality of slavedevices is stopped.

Thereby, it is not possible to cause each piece of equipment of the FAsystem to perform a desired operation, which results in, for example,the generation of defective products manufactured in the FA system. Inaddition, when all equipment of which the operation is controlled by thecontroller is stopped in association with the stopping of thecontroller, productivity deteriorates.

Therefore, an objective of the present invention is to provide a controltechnique capable of continuing control for slave devices even when acontroller having performed control for the slave devices is stopped.

A control system includes a field bus to which slave devices arelinearly connected through a communication cable, a first controller,and a second controller. The first controller is connected to one end ofthe field bus, and the second controller is connected to the other endof the field bus.

Each of the first controller and the second controller includes acontrol frame generation part and a transception part. The control framegeneration part generates a control frame to be provided to the slavedevices. The transception part transmits and receives the control frameto and from the slave devices.

One of the first controller and the second controller generates thecontrol frame by the control frame generation part, transmits thegenerated control frame from the transception part, and the other oneperforms loopback communication of the control frame by the transceptionpart.

In this configuration, the first controller and the second controllerhave a configuration in which a control frame can be provided to theslave devices. In addition, the first controller and the secondcontroller also have a configuration in which a control frame can besimply looped back. Therefore, even when the first controller cannotgenerate and transmit a control frame, the second controller generatesand transmits the control frame. In contrast, even when the secondcontroller cannot generate and transmit a control frame, the firstcontroller generates and transmits the control frame.

In addition, the control system includes a data communication networkthat connects the first controller and the second controller withoutgoing through the slave devices.

Therefore, the first controller and the second controller directlyconfirm mutual operation conditions through the data communicationnetwork.

Further, in the control system, when the first controller generates andtransmits the control frame and the second controller performs loopbackcommunication of the control frame, the following processing isexecuted. The second controller transmits an operation confirmationsignal to the first controller through the data communication network.The second controller starts generation and transmission of the controlframe when a response signal to the operation confirmation signal is notable to be received.

Therefore, the second controller easily and reliably confirms that thefirst controller generates and transmits a control frame and cannotgenerate and transmit the control frame due to some reasons.

Further, in the control system, the second controller observes thecontrol frame and may start generation and transmission of the controlframe when the control frame is not able to be received over apredetermined period of time.

In this configuration, the second controller confirms that the firstcontroller has stopped generation and transmission of a control frameinclusive of information received from a network to which the pluralityof slave devices is connected.

In addition, the control system includes a user interface device whichis connected to the data communication network and receives an operationinput of switching of control between the first controller and thesecond controller. When the first controller generates and transmits thecontrol frame and the second controller performs loopback communicationof the control frame, the first controller stops generation andtransmission of the control frame and starts the loopback communicationof the control frame when receiving a command for the switching of thecontrol from the user interface device, and the second controller maystop the loopback communication of the control frame and start thegeneration and the transmission of the control frame when receiving acommand for the switching of the control from the user interface device.

In this configuration, generation and transmission of a control frameare switched from the first controller to the second controller inresponse to an operation input.

Further, in the control system, the first controller and the secondcontroller transmit and receive a switching confirmation signal andmutually confirm the switching. After this configuration, the firstcontroller stops the generation and the transmission of the controlframe and starts the loopback communication of the control frame, andthe second controller may stop the loopback communication of the controlframe and start the generation and the transmission of the controlframe.

In this configuration, a timing when the first controller stopsgeneration and transmission of a control frame and a timing when thesecond controller starts generation and transmission of a control frameare properly adjusted.

Further, in the control system, the control frame generation part andthe transception part may be formed of different semiconductor devices.

In this configuration, the above-described switching is reliablyrealized.

Further, in the control system, the control frame generation part isconstituted by a computation element that executes a generation programfor the control frame, and the transception part may be constituted by asemiconductor element that exclusively performs transmission andreception of the control frame.

In this configuration, the control frame generation part and thetransception part are realized by elements appropriate for therespective processes.

According to the invention, it is possible to continue control for slavedevices even when a controller having performed control on the slavedevices is stopped.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a configuration of a device in a controlsystem.

FIG. 2 is a block diagram showing a configuration of hardware in acontroller.

FIG. 3 is a block diagram showing a configuration related to a datacommunication in the controller.

FIG. 4 is a diagram showing a schematic data configuration of controldata.

FIG. 5 is a diagram showing an outline of data communication for storinga control frame.

FIG. 6 is a diagram showing the state of data transmission in thecontroller in a run mode.

FIG. 7 is a flowchart showing a schematic process executed by thecontroller in a run mode.

FIG. 8 is a diagram showing the state of data transmission in thecontroller in a data acquisition mode.

FIG. 9 is a flowchart showing a schematic process executed by thecontroller in a data acquisition mode.

FIG. 10 is a flowchart showing a diagnosis frame transmission process ofthe controller in a run mode.

FIG. 11 is a flowchart showing a process of receiving and transmittingthe diagnosis frame by the controller in a data acquisition mode.

FIG. 12 is a diagram showing a configuration of a device in the controlsystem.

FIG. 13 is a diagram showing the state of data transmission in thecontroller in a run mode.

FIG. 14 is a diagram showing the state of data transmission in thecontroller in a data acquisition mode.

FIG. 15 is a diagram showing an example of an outline of redundancy ofthe controller.

FIG. 16 is a diagram showing the state of data transmission in thecontroller when switching from a data acquisition mode to a run mode.

FIG. 17 shows a first mode for determining switching using only aresponse of a beacon.

FIG. 18 shows a second mode for determining switching using only aresponse of a beacon.

FIG. 19 shows a mode for determining switching using an observationresult of a control frame and a response of a beacon.

FIG. 20 is a diagram showing the state of data transmission in acontroller after switching to a run mode.

FIG. 21 is a diagram showing the state of data transmission in modeswitching between two controllers connected to a control network.

FIG. 22 is a flowchart showing a schematic process of mode switchingexecuted by two controllers.

FIG. 23 is a diagram showing an example of a case that can be dealt withby redundancy of a cable.

FIG. 24 is a flowchart of a process of the controller in a run modecorresponding to redundancy of a cable.

FIG. 25 is a flowchart of a process of the controller in a dataacquisition mode corresponding to redundancy of a cable.

FIG. 26 is a diagram showing a configuration of a device in the controlsystem in a case where abnormality detection is executed by a controllerin a data acquisition mode.

FIG. 27 is a block diagram showing a configuration related to datacommunication in a controller in a data acquisition mode.

DESCRIPTION OF EMBODIMENTS

A control system and a control method according to an embodiment of thepresent invention will be described with reference to the accompanyingdrawings. In the present embodiment, description will be given using afactory automation (FA) system as an example of a control system,specifically, an FA system having a control network according toEtherCAT (registered trademark) as an example of a network standard.However, a configuration of the present invention can also be applied toother control systems that execute communication according to the samenetwork standard as EtherCAT.

(Configuration of Control System) FIG. 1 is a diagram showing aconfiguration of a device in a control system. As shown in FIG. 1, acontrol system 1 includes a controller 11, a controller 12, a pluralityof slave devices 21, 22, and 23, a plurality of communication cables 31,32, 33, 34, and 35, a database device 40, a user interface device (UIdevice) 50, and an information communication network 60. The controller11 corresponds to a “first controller” of the present invention, and thecontroller 12 corresponds to a “second controller” of the presentinvention.

The database device 40 stores a control frame and a diagnosis frame thatare described below. In addition, the database device 40 executes aprocess related to abnormality detection of a control network using thecontrol frame or the diagnosis frame which are acquired and stored bythe control system 1. For example, the process related to abnormalitydetection which is executed by the database device 40 includes at leastone of abnormality diagnosis, abnormality notification, abnormality signestimation, data trace, and load monitoring of a control network, andcan be realized by a known method.

The UI device 50 transmits a user program to the controller 11 and thecontroller 12. Meanwhile, it is also possible to create a user programin the UI device 50. In addition, the UI device 50 sets a control valueand a process for the controller 11 and the controller 12.

The controller 11 is connected to the slave device 21 through thecommunication cable 31. The slave device 21 is connected to the slavedevice 22 through the communication cable 32. The slave device 22 isconnected to the slave device 23 through the communication cable 33. Theslave device 23 is connected to the controller 12 through thecommunication cable 34.

That is, the controller 11, the slave device 21, the slave device 22,the slave device 23, and the controller 12 are linearly connected inthis order. In other words, the plurality of slave devices 21, 22, and23 is connected in order from a first end to a second end with thecontroller 11 as the first end and the controller 12 as the second end.In addition, the controller 12 is connected to the controller 11 throughthe communication cable 35. Such a field bus of the control network isconstituted in accordance with such a connection mode of thecommunication cables. In this control network, data is communicated inaccordance with a network standard of EtherCAT (registered trademark)using Ethernet (registered trademark). Meanwhile, specific contents ofcommunication will be described later.

The controller 11, the controller 12, the database device 40, and the UIdevice 50 are connected to each other through the informationcommunication network 60. The information communication network 60performs communication according to a general-purpose network standardsuch as Ethernet and realizes a data link between the controller 11, thecontroller 12, the database device 40, and the UI device 50. Meanwhile,the control system 1 of the present invention may include at least aportion of a control network.

(Configuration of Controller)

The controller 11 and the controller 12 have the same configuration.FIG. 2 is a block diagram showing a configuration of hardware in acontroller. Meanwhile, in FIG. 2, the controller 11 and the controller12 have the same configuration, and thus the controllers will bedescribed as being a controller 10.

As shown in FIG. 2, the controller 10 includes a CPU 101, a transceptionpart 102, a high-order communication part 103, a shared memory 104, aprogram memory 105, and a system bus 110. The transception part 102, thehigh-order communication part 103, the shared memory 104, and theprogram memory 105 are connected to each other by the system bus 110.

The transception part 102 is realized by an ASIC or the like and isrealized by a dedicated IC different from the CPU 101. Meanwhile, thetransception part 102 may be realized by a FPGA or the like. Thetransception part 102 is connected to the control network and executestransmission and reception of a control frame.

The high-order communication part 103 is realized by a general-purposecommunication IC. The high-order communication part 103 is connected tothe information communication network 60 and executes transmission andreception through the information communication network 60.

The shared memory 104 stores various data for control received from theinformation communication network 60, PDO data constituting a controlframe, and the like. The PDO data is constituted by a data groupincluding output data which are output to the plurality of slave devices21, 22, and 23 and input data which are input from the plurality ofslave devices 21, 22, and 23.

A system program in which basic control of the controller 10 is recordedand a user program for control which is written by the UI device 50 arestored in the program memory 105. The user program may be differentbetween a controller in a run mode and a controller in a dataacquisition mode, which will be described later, and may be capable ofselectively realizing both the run mode and the data acquisition mode.

FIG. 3 is a block diagram showing a configuration related to a datacommunication in the controller. FIG. 4 is a diagram showing a schematicdata configuration of control data.

As shown in FIG. 3, the CPU 101 realizes a PLC control, an EtherCATstack, an Ether driver, and an Ether driver for high-ordercommunication.

The EtherCAT stack, the Ether driver, and the Ether driver forhigh-order communication are realized by the CPU 101 reading out andexecuting a system program from the program memory 105. The PLC controlis realized by the CPU 101 reading out and executing a user program forcontrol from the program memory 105.

The PLC control is performed to generate PDO data using data stored inthe shared memory 104. That is, the PLC control is performed to generatethe PDO data using input data such as measured values received from theslave devices 21, 22, and 23, calculation results based on the inputdata, a user program, control information obtained from the UI device50, and the like. As shown in FIG. 4, the PDO data includes a dataregion DG21 for the slave device 21, a data region DG22 for the slavedevice 22, and a data region DG23 for the slave device 23. The dataregion DG21 for the slave device 21 is a writing region for output datawhich is output to the slave device 21 and input data which is inputfrom the slave device 21, the data region DG22 for the slave device 22is a writing region for output data which is output to the slave device22 and input data which is input from the slave device 22, and the dataregion DG23 for the slave device 23 is a writing region for output datawhich is output to the slave device 23 and input data which is inputfrom the slave device 23. Meanwhile, in the slave devices 21, 22, and23, the data regions for the slave devices are only writing regions ofoutput data which are output from the slave devices when the slavedevices are devices, such as sensors, which do not require input dataand require output data for control. On the other hand, in the slavedevices 21, 22, and 23, the data regions for the slave devices are onlywriting regions of input data which are input to the slave devices whenthe slave devices are devices, such as switches, which require inputdata for control and do not require output data for control.

The PLC control is performed to execute scheduling of transmission ofcontrol data. The PLC control is performed to transmit PDO data to theEtherCAT stack. In addition, the PLC control is performed to extractinput data associated from the slave devices 21, 22, and 23 from the PDOdata received from the EtherCAT stack and to store the extracted inputdata in the shared memory 104.

The EtherCAT stack attaches an EtherCAT header (ECH in FIG. 4) to PDOdata and transmits the PDO data to the Ether driver. In contrast, theEtherCAT stack extracts PDO data from frame data (ECH+PDO in FIG. 4)from the Ether driver and transmits the extracted PDO data to the PLCcontrol.

The Ether driver attaches the Ethernet header (EH in FIG. 4) and CRCdata (CRC in FIG. 4) to frame data (ECH+PDO in FIG. 4) received from theEtherCAT stack and outputs the frame data to a transmission part 121 ofthe transception part 102 as a control frame. In contrast, the Etherdriver extracts frame data (ECH+PDO in FIG. 4) corresponding to theEtherCAT from the control frame (data shown in FIG. 4) received from areception part 122 of the transception part 102, and transmits theextracted frame data to the EtherCAT stack.

Meanwhile, the CPU 101 executes transmission and reception with respectto the information communication network 60 through the high-ordercommunication part 103 using an Ether driver for high-ordercommunication. Thereby, the CPU 101 receives a system program, a userprogram, and various data from the UI device 50 through the informationcommunication network 60 and stores the received programs and data inthe program memory 105 or the shared memory 104. Communication with theinformation communication network 60 is performed according to ageneral-purpose Ethernet or the like, and description thereof will beomitted.

(Configuration of Transception Part 102)

The transception part 102 includes the transmission part 121, thereception part 122, and an interface (IF) 123. The transmission part 121and the reception part 122 are realized by individual ICs. The IF 123realizes physical connection to a communication cable and includes atleast two ports.

The transmission part 121 transmits a control frame received from theCPU 101 to the control network through the IF 123. In this case, thetransmission part 121 transmits the control frame with a time stampprovided thereto. In addition, the transmission part 121 can alsotransmit a control frame copied from the reception part 122 shown nextto the control network through the IF 123. Further, the transmissionpart 121 can generate a diagnosis frame to be described later andtransmit the generated diagnosis frame to the control network throughthe IF 123 at a predetermined time.

The reception part 122 transmits the control frame received from thecontrol network through the IF 123 to the CPU 101. The reception part122 can also copy the control frame. The reception part 122 can alsotransmits the copied control frame to the transmission part 121 or thehigh-order communication part 13. In this case, the reception part 122directly transmits the copied control frame to the transmission part 121or the high-order communication part 13 without going through the CPU101.

(Abnormality Detection)

FIG. 5 is a diagram showing an outline of data communication for storinga control frame. In FIG. 5, a bold arrow indicates a flow of the controlframe.

In a process of collecting a control frame for abnormality detection,the controller 11 is set to be in a run mode, and the controller 12 isset to be in a data acquisition mode. The controller 11 corresponds to a“first controller” of the present invention, and the controller 12corresponds to a “second controller” of the present invention.

The controller 11 in a run mode executes schedule management oftransmission and reception of a control frame, calculation using inputdata received from the slave devices 21, 22, and 23, generation ofoutput data using a calculation result, and generation of a controlframe. That is, the controller 11 in a run mode executes control of datacommunication with the plurality of slave devices 21, 22, and 23 throughcyclic communication using a control network at high speed.

The controller 12 in a data acquisition mode receives a control frameand transmits the received control frame to the database device 40 ofthe information communication network 60 without executing management ofcontrol data communication with the plurality of slave devices 21, 22,and 23 as in the controller 11.

When the controller 11 generates a control frame as shown in FIG. 4, thecontroller transmits the generated control frame to the control network.That is, the controller 11 transmits the control frame through thecommunication cable 31.

The slave device 21 receives the control frame through the communicationcable 31. The slave device 21 acquires output data for the slave device21 which is described in the control frame and writes input dataacquired by the slave device 21 in the control frame. Meanwhile, theslave device 21 controls a control target device connected to the slavedevice 21 based on output data. In addition, the slave device 21acquires a measured value from the control target device and sets themeasured value as input data in the next control cycle.

The slave device 21 imparts a time stamp to the control frame. The slavedevice 21 transmits the control frame through the communication cable32.

The slave device 22 receives the control frame through the communicationcable 32. The slave device 22 acquires output data for the slave device22 which is described in the control frame and writes input dataacquired by the slave device 22 in the control frame. Meanwhile, theslave device 22 controls a control target device connected to the slavedevice 22 based on output data. In addition, the slave device 22acquires a measured value from the control target device and sets themeasured value as input data in the next control cycle.

The slave device 22 imparts a time stamp to the control frame. The slavedevice 22 transmits the control frame through the communication cable33.

The slave device 23 receives the control frame through the communicationcable 33. The slave device 23 acquires output data for the slave device23 which is described in the control frame and writes input dataacquired by the slave device 23 in the control frame. Meanwhile, theslave device 23 controls a control target device connected to the slavedevice 23 based on output data. In addition, the slave device 23acquires a measured value from the control target device and sets themeasured value as input data in the next control cycle.

The slave device 23 imparts a time stamp to the control frame. The slavedevice 23 transmits the control frame through the communication cable34.

The controller 12 receives the control frame through the communicationcable 34. The controller 12 copies the control frame and transmits thecontrol frame through the communication cable 35. In this case, thecontroller 12 imparts a time stamp to the control frame. The controlframe is received by the controller 11 through the communication cable35. In addition, the controller 12 transmits the copied control frame tothe database device 40 connected through the information communicationnetwork 60.

(Specific Process of Controller 11 in Run Mode)

The controller 11 set to be in a run mode specifically executes the nextprocess. The setting of the controller to be in a run mode is executedin response to, for example, a control command received from the UIdevice 50. FIG. 6 is a diagram showing the state of data transmission inthe controller in a run mode.

In the controller 11, the CPU 101 generates a control frame by PLCcontrol, an EtherCAT stack, and an Ether driver using a data groupstored in the shared memory 104, as described above. This control framegeneration process is executed in accordance with a control cycledetermined through PLC control. The CPU 101 outputs the control frame tothe transmission part 121 of the transception part 102.

The transmission part 121 transmits the control frame to thecommunication cable 31 through the IF 123 in the above-described controlcycle.

On the other hand, in the controller 11, the reception part 122 of thetransception part 102 receives a control frame returned from the controlnetwork through the communication cable 35 and the IF 123. The receptionpart 122 outputs the control frame to the CPU 101.

As described above, the CPU 101 extracts PDO data from the control frameby an Ether driver, an EtherCAT stack, and PLC control. The CPU 101stores the PDO data in the shared memory 104. Meanwhile, the CPU 101 mayextract input data received from the plurality of slave devices 21, 22,and 23 from the PDO data and store only the input data in the sharedmemory 104.

The controller 11 repeatedly executes the generation and thetransmission and reception of the control frame and the storage of PDOdata returned from the control network in accordance with theabove-described control cycle.

That is, the controller 11 executes a process shown in FIG. 7. FIG. 7 isa flowchart showing a schematic process executed by the controller in arun mode. Meanwhile, the process shown in FIG. 7 is executed by the CPU101 and the transception part 102, but can be executed by only the CPU101.

As shown in FIG. 7, the controller 11 reads out data groups required fora current control frame including the previous PDO data from the sharedmemory 104 (S101). The controller 11 generates current PDO data usingthese data groups (S102). The controller 11 generates a control frameusing the PDO data (S103). The controller 11 sets a transmission timefrom a control cycle (S104). The controller 11 transmits the controlframe in synchronization with the transmission time (S105). Thecontroller 11 receives a control frame returned from the control network(S106). The controller 11 extracts PDO data from the returned controlframe (S107). The controller 11 writes the PDO data in the shared memory104 (S108). When these processes are terminated, the controller 11returns to step S101 to repeat the process.

(Specific Process of Controller 12 in Data Acquisition Mode)

The controller 12 set to be in a data acquisition mode specificallyexecutes the next process. The setting of the controller to be in a dataacquisition mode is executed in response to, for example, a controlcommand received from the UI device 50. FIG. 8 is a diagram showing thestate of data transmission in the controller in a data acquisition mode.

In the controller 12, a reception part 122′ of the transception part102′ receives a control frame transmitted from the control network, thatis, having passed through all of the slave devices 21, 22, and 23through the communication cable 34 and an IF 123′. The reception part122′ copies the control frame. The reception part 122′ outputs thecontrol frame to a CPU 101′ and outputs the control frame to atransmission part 121′. PDO data which is input to the CPU 101′ isstored in the shared memory 104, similar to the CPU 101.

The transmission part 121′ outputs the control frame to thecommunication cable 35 through the IF 123′. That is, the reception part122′ and the transmission part 121′ execute loopback of the controlframe in the control network.

In addition, the reception part 122′ transmits the control frame to thehigh-order communication part 103′. This transmission is performedusing, for example, a direct memory access (DMA) transmission method.The high-order communication part 103′ transmits the control frame tothe database device 40 of the information communication network 60through an IF 130′. Meanwhile, in this case, the controller 12 imparts atime stamp to the control frame.

The controller 12 executes return of the control frame and transmissionto the information communication network 60 every time a control frameis received.

That is, the controller 12 executes a process shown in FIG. 9. FIG. 9 isa flowchart showing a schematic process executed by the controller in adata acquisition mode. Meanwhile, the process shown in FIG. 9 isexecuted by the CPU 101′, the transception part 102′ and the high-ordercommunication part 103′, but can also be executed by only the CPU 101′.

As shown in FIG. 9, the controller 12 receives a control frametransmitted from the control network (S201). The controller 12 copiesthe control frame (S202). The controller 12 returns the control frame tothe control network (S203). The controller 12 transmits the controlframe to the database device 40 of the information communication network60 (S211). The controller 12 extracts PDO data from the control frame(S221) and stores the extracted PDO data in a shared memory 104′ (S222).Meanwhile, when the redundancy of the controller to be described lateris not required, the controller 12 may not extract and store the PDOdata.

As described above, in the control system 1, the controller 11 in a runmode does not perform storage of a control frame for abnormalitydetection and transmission of the control frame to the informationcommunication network 60. That is, the controller 11 in a run modeexclusively executes cyclic control of the plurality of slave devices21, 22, and 23.

On the other hand, the controller 12 in a data acquisition mode does notperform management of transmission and reception of a control frame.That is, the controller 12 in a data acquisition mode exclusivelyexecutes storage of a control frame for abnormality detection andtransmission of the control frame to the information communicationnetwork 60.

With such a configuration, the control system 1 can inhibit reduction inthe amount of acquisition of control frames for abnormality detectionwhile reliably performing communication of a control frame between thecontroller and the plurality of slave devices, irrespective of theamount of data communicated through the control network.

Further, in the control system 1, the controller 12 in a dataacquisition mode is connected to the ends of the plurality of slavedevices 21, 22, and 23 starting from the controller 11 in a run mode.Therefore, the controller 12 can receive a control frame including PDOdata updated by all of the slave devices 21, 22, and 23 in a currentcontrol cycle. Thereby, the controller 12 can efficiently acquire acontrol frame updated to the latest state.

Further, in the control system 1, the controller is constituted by theCPU and the transception part, and thus it is possible to inhibit adelay of return of the above-described control frame and to inhibitlengthening of a control cycle due to connection of the controller in adata acquisition mode. In addition, a CPU is not used at the time oftransmitting a control frame to the database device 40 of theinformation communication network 60, and thus a load of the CPU isreduced.

(Transmission and Storage of Diagnosis Frame)

Meanwhile, in the above-described configuration and process, a mode inwhich a control frame periodically communicated in accordance with acontrol cycle is stored and transmitted has been described, but it isalso possible to generate a diagnosis frame and store and transmit thediagnosis frame.

FIG. 10 is a flowchart showing a diagnosis frame transmission process ofthe controller in a run mode. As shown in FIG. 10, the controller 11generates a diagnosis frame (S121). The controller 11 detects whether ornot it is a transmission timing for the diagnosis frame. Thetransmission timing for the diagnosis frame is set in advance atpredetermined time intervals or is determined in response to atransmission request for the diagnosis frame which is received from theUI device 50. When it is a transmission timing for the diagnosis frame(S122: YES) and a control frame is being transmitted (S123: NO), thecontroller 11 transmits the diagnosis frame to the control network(S124).

FIG. 11 is a flowchart showing a process of receiving and transmittingthe diagnosis frame by the controller in a data acquisition mode. Asshown in FIG. 11, the controller 12 receives the diagnosis frame (S231).The controller 12 transmits the diagnosis frame to the database device40 of the information communication network 60 (S232). In this case,when the controller 12 detects being the diagnosis frame, the controllermay not perform copying and return as in the above-described controlframe.

With such a configuration and process, the control system 1 can transmitand store a diagnosis frame for abnormality detection while reliablyperforming communication of a control frame between the controller andthe plurality of slave devices. Therefore, it is possible to acquire alarger amount of frame data for abnormality detection and acquire datafor performing detailed abnormality detection.

Further, the diagnosis frame transmission process in the above-describedcontroller 11 is executed by the transception part 102, so that it ispossible to inhibit an increase in a processing load of the CPU 101 ofthe controller 11 due to the use of a diagnosis frame.

Further, in the above description, a mode in which the controller 11does not transmit a control frame and a diagnosis frame to the databasedevice 40 of the information communication network 60 has beendescribed. However, the controller 11 may transmit a control frame and adiagnosis frame to the database device 40 of the informationcommunication network 60. Here, a control frame and a diagnosis frameare not transmitted to the, database device 40 of the informationcommunication network 60, so that it is possible to secure acommunication band between the CPU 101 of the controller 11 and the UIdevice 50 through the information communication network 60. Therefore,communication of control data between the UI device 50 and the CPU 101of the controller 11 can be performed reliably and at high speed.

Meanwhile, in the above description, the controller 11 and thecontroller 12 are connected to each other through the communicationcable 35. However, the communication cable 35 can also be omitted. FIG.12 is a diagram showing a configuration of a device in the controlsystem. As shown in FIG. 12, a control system 1A includes a controller11A, a controller 12A, a plurality of slave devices 21, 22, and 23, aplurality of communication cables 31, 32, 33, and 34, a database device40, a user interface device (UI device) 50, and an informationcommunication network 60. The control system 1A shown in FIG. 12 has aconfiguration in which a communication cable 35 is omitted with respectto the control system 1 shown in FIG. 1. Therefore, hereinafter, onlynew parts required to be described and different from those of thecontrol system shown in FIG. 1 will be described.

The controller 11A, the slave device 21, the slave device 22, the slavedevice 23, and the controller 12A are linearly connected in this order.In other words, the plurality of slave devices 21, 22, and 23 isconnected in order from a first end to a second end with the controller11A as the first end and the controller 12A as the second end. However,the controller 11A and the controller 12A are not directly connected toeach other. In this case, a control frame transmitted from thecontroller 11A and having reached the controller 12A is looped back bythe controller 12A and returns to the controller 11A through the slavedevice 23, the slave device 22, and the slave device 21 in this order.

(Specific Process of Controller 11A in Run Mode)

The controller 11A set to be in a run mode specifically executes thenext process. FIG. 13 is a diagram showing the state of datatransmission in the controller in a run mode.

In the controller 11A, the CPU 101 generates a control frame by PLCcontrol, an EtherCAT stack, and an Ether driver using a data groupstored in the shared memory 104, as described above. This control framegeneration process is executed in accordance with a control cycledetermined through PLC control. The CPU 101 outputs the control frame tothe transmission part 121 of the transception part 102.

The transmission part 121 transmits the control frame to thecommunication cable 31 through an IF 123 in the above-described controlcycle.

On the other hand, in the controller 11, the reception part 122 of thetransception part 102 receives a control frame returned from the controlnetwork through the communication cable 31 and the IF 123. The receptionpart 122 outputs the control frame to the CPU 101.

(Specific Process of Controller 12A in Data Acquisition Mode)

The controller 12A set to be in a data acquisition mode specificallyexecutes the next process. FIG. 14 is a diagram showing the state ofdata transmission in the controller in a data acquisition mode.

In the controller 12A, a reception part 122′ of a transception part 102′receives a control frame transmitted from the control network throughthe communication cable 34 and an IF 123′. The reception part 122′copies the control frame. The reception part 122′ outputs the controlframe to a CPU 101′ and outputs the control frame to a transmission part121′.

The transmission part 121′ outputs the control frame to thecommunication cable 34 through an IF 123′. That is, the reception part122′ and the transmission part 121′ execute loopback of the controlframe in the control network.

In addition, the reception part 122′ transmits the control frame to thehigh-order communication part 103′. This transmission is performedusing, for example, a direct memory access (DMA) transmission method.The high-order communication part 103′ transmits the control frame tothe database device 40 of the information communication network 60through an IF 130′. Meanwhile, in this case, the controller 12 imparts atime stamp to the control frame.

The controller 12 loops back the control frame and executes transmissionto the information communication network 60 every time a control frameis received.

Even the control system 1A having such a configuration can inhibit areduction in the amount of acquisition of control frames for abnormalitydetection while reliably performing communication of a control framebetween the controller and the plurality of slave devices, irrespectiveof the amount of data communicated through the control network.

(Redundancy of Controller)

The control system 1 having the above-described configuration can copewith the redundancy of a controller. In general, the redundancy of acontroller is a configuration in which controllers capable ofgenerating, transmitting, and receiving control frames are connected toboth ends of a control network having the plurality of slave devices 21,22, and 23, respectively (similar configuration as those in FIGS. 1 and12). Further, in the redundancy of a controller, any one of thecontrollers at both ends is used for the generation of a control frameand schedule management.

FIG. 15 is a diagram showing an example of an outline of redundancy ofthe controller. FIG. 15 shows a mode in which the controller 11 failsduring execution of a run mode and the controller 12 switches from adata acquisition mode to a run mode. In FIG. 15, a black bold arrowindicates a transmission state of a beacon, and a white bold arrowindicates a transmission state of a control frame.

As shown in FIG. 15, the controller 12 transmits a beacon (correspondingto an “operation confirmation signal” of the present invention) to thecontroller 11 through the information communication network 60. Whenthere is no response signal of the beacon, the controller 12 switchesfrom a data acquisition mode (a P mode in FIG. 15) to a run mode (an Rmode in FIG. 15). In addition, the controller 12 generates a controlframe for the control network to which the plurality of slave devices21, 22, and 23 is connected, and transmits the control frame to thecontrol network. When the controller 11 has the above-describedconfiguration, loopback communication of a control frame can beperformed by the transception part 102 even when the CPU 101 fails.

(Specific Process of Controller 12 that Switches from Data AcquisitionMode to Run Mode)

FIG. 16 is a diagram showing the state of data transmission in thecontroller when switching from a data acquisition mode to a run mode. InFIG. 16, a black bold arrow indicates a transmission state of a beacon,and a white bold arrow indicates a transmission state of a controlframe.

The controller 12 sequentially executes the copying and loopback of theabove-described control frame, the transmission to the database device40 of the information communication network 60, and the storage of PDOdata in the shared memory 104 in a period in which the controller is setto be in a data acquisition mode.

Along with these processes, the CPU 101 of the controller 12 generates abeacon in PLC control. In this case, the CPU 101 generates a beacon at apreset cycle for operation confirmation. The cycle for operationconfirmation is set to a constant multiple (for example, approximatelytwo times to five times) of the control cycle of the control network.Meanwhile, the constant is an example and may be any of other values. Inaddition, the CPU 101 detects that the output of a control frame hasbeen stopped when a control frame is not output from the transceptionpart 102 over a predetermined period of time, and generates a beacon.

An Ether driver for high-order communication attaches an Ethernet headerwith the controller 11 as a reception destination to the beacon, andoutputs the beacon to the high-order communication part 103. Thehigh-order communication part 103 outputs the beacon to the informationcommunication network 60 through an IF 130.

In PLC control in the CPU 101 of the controller 12, switching from adata acquisition mode to a run mode is executed when a response signalof a beacon cannot be detected.

Specifically, the controller 12 executes a process as shown in any oneof the following FIGS. 17, 18, and 19.

FIG. 17 is a flowchart showing a schematic process executed by thecontroller switching from a data acquisition mode to a run mode. FIG. 17shows a first mode for determining switching using only a response of abeacon.

As shown in FIG. 17, the controller 12 receives slave information, thatis, information of the plurality of slave devices 21, 22, and 23connected to the control network (S300). Such information of theplurality of slave devices 21, 22, and 23 is acquired when thecontroller 11 constructs the control network, is transmitted from thecontroller 11, and is received by the controller 12. Meanwhile, thisprocess is a preliminary process for switching from a data acquisitionmode to a run mode, but is not an essential process in switching from adata acquisition mode to a run mode, and the process may be realized byanother method.

The controller 12 generates a beacon and transmits the generated beaconto the controller 11 through the information communication network 60(S301). When there is a response signal to the beacon (S302: NO), thecontroller 12 repeatedly transmitting the beacon at the above-describedcycle for operation confirmation.

When there is no response signal to the beacon (S302: YES), thecontroller 12 switches from a data acquisition mode to a run mode(S303).

FIG. 18 is a flowchart showing a schematic process executed by thecontroller switching from a data acquisition mode to a run mode. FIG. 18shows a second mode for determining switching using only a response of abeacon.

As shown in FIG. 18, the controller 12 generates a beacon and transmitsthe generated beacon to the controller 11 through the informationcommunication network 60 (S301). When there is a response signal to thebeacon (S302: NO), the controller 12 repeatedly transmitting the beaconat the above-described cycle for operation confirmation.

When there is no response signal to the beacon (S302: YES), thecontroller 12 counts up the number of times there is no response to thetransmission of the beacon (S311). When a counted value has not reacheda switching threshold value (S312: NO), the controller 12 repeatedlytransmitting the beacon at the above-described cycle for operationconfirmation.

When the counted value has reached the switching threshold value (S312:YES), the controller 12 switches from a data acquisition mode to a runmode (S303).

The process shown in FIG. 18 is used, and thus switching of an erroneousmode due to a communication error of a beacon through the informationcommunication network 60, or the like is inhibited.

FIG. 19 is a flowchart showing a schematic process executed by thecontroller switching from a data acquisition mode to a run mode. FIG. 19shows a mode for determining switching using an observation result of acontrol frame and a response of a beacon.

The controller 12 observes a control frame (S401). When a control framecan be received (S402: NO), the controller 12 repeatedly observes thecontrol frame.

When a control frame cannot be received for a predetermined period oftime (S402: YES), the controller 12 generates a beacon and transmits thegenerated beacon to the controller 11 through the informationcommunication network 60 (S301). Here, the predetermined period of timeis, for example, a constant multiple of a control cycle. When there is aresponse signal to the beacon (S302: NO), the controller 12 repeatedlytransmitting the beacon at the above-described cycle for operationconfirmation.

When there is no response signal to the beacon (S302: YES), thecontroller 12 switches from a data acquisition mode to a run mode(S303).

The process shown in FIG. 19 is used, and thus it is possible to detecta failure of the controller 11, and the like based on a communicationstate of the control frame in the control network and the beacon throughthe information communication network 60. Thereby, the accuracy ofdetection for the controller 11 is improved.

In this manner, when the controller switches from a data acquisitionmode to a run mode, the controller 12 executes a process as shown inFIG. 20. FIG. 20 is a diagram showing the state of data transmission ina controller after switching to a run mode. The process shown in FIG. 20is a process in which a main body of the process is replaced from thecontroller 11 to the controller 12, with respect to the process shown inFIG. 6. Therefore, description of a detailed process will be omitted.That is, when the controller 12 switches to a run mode, the controllerexecutes a process similar to the process executed by the controller 11in the control network.

As described above, the above-described configuration and process areused, and thus it is possible to continue control using the controlnetwork by the controller 12 even when the controller 11 cannot performthe generation of a control frame and schedule management due to afailure or the like. That is, a stop period of control for the controlnetwork hardly occurs.

In this case, the controller 12 stores PDO data in the shared memory 104in a data acquisition mode as described above. Therefore, the controller12 already holds PDO data so far when switching to a run mode. Thereby,the controller 12 can rapidly and reliably generate a control frame.

Further, as described above, the controller 12 acquires information ofthe plurality of slave devices 21, 22, and 23 from the controller 11 andstores the acquired information in the shared memory 104 beforeswitching to a run mode. Thereby, the controller 12 does not need toacquire the information of the plurality of slave devices 21, 22, and 23from the plurality of slave devices 21, 22, and 23 again afterswitching. Therefore, it is possible to more rapidly and reliablygenerate a control frame.

Further, in the controller 11, when the CPU 101 fails or runs away andthe transception part 102 is normal, a control frame is copied by thetransception part 102 in the controller 11. In addition, the copiedcontrol frame is transmitted to the database device 40 of theinformation communication network 60 through the transception part 102and the high-order communication part 103. Thereby, the transmission ofa control frame for abnormality detection is continued.

(Specific Process of Mode Switching Between Controller 11 and Controller12)

FIG. 21 is a diagram showing the state of data transmission in modeswitching between two controllers connected to a control network. InFIG. 21, a black bold arrow indicates a transmission state of aswitching command signal, and a hatched bold arrow indicates atransmission state of a switching confirmation signal.

The UI device 50 transmits a switching command signal to the controller11 operating in a run mode and the controller 12 operating in a dataacquisition mode through the information communication network 60. Whenthe controller 11 and the controller 12 receive a switching commandsignal, the controllers transmit and receive the switching confirmationsignal to and from each other through the information communicationnetwork 60.

Thereafter, the controller 11 stops a run mode and starts a dataacquisition mode. In synchronization with this, the controller 12 startsa run mode and stops a data acquisition mode.

FIG. 22 is a flowchart showing a schematic process of mode switchingexecuted by two controllers.

When the controller 11 receives a switching command signal (S411), thecontroller transmits a control stop notice signal which is a switchingconfirmation signal to the controller 12 (S412). The control stop noticesignal may include, for example, a time when control is stopped, and thelike.

When the controller 12 receives a switching command signal (S421), thecontroller waits for the reception of the control stop notice signal andreceives the control stop notice signal (S422). The controller 12analyzes the control stop notice signal and transmits the control startnotice signal to the controller 11 (S423).

When the controller 11 receives the control start notice signal (S413),the controller stops control. Thereby, the controller 11 switches from arun mode to a data acquisition mode. Thereafter, the controller 11observes a control frame and confirms whether or not the control framecan be received (S415).

The controller 12 observes a control frame after transmitting thecontrol start notice signal and confirms that a control frame has notbeen received (S424). Thereafter, the controller 12 starts switchingfrom a data acquisition mode to a run mode, generation of a controlframe, and transmission and reception of a control frame to the controlnetwork (S425).

In this manner, in the control system 1, a controller in a run mode anda controller in a data acquisition mode can be mutually switched underthe control of the UI device 50. Thereby, for example, rewriting andupdating of firmware can be realized while continuing control of theplurality of slave devices 21, 22, and 23. For example, rewriting offirmware is performed on the controller 12 in a data acquisition mode,and switching between a run mode and a data acquisition mode withrespect to the controller 11 and the controller 12 is executed. Inaddition, rewriting of firmware is performed on the controller 11 set tobe in a data acquisition mode.

In this case, the controller in a data acquisition mode hardly has aload on the CPU 101 for control of the plurality of slave devices.Therefore, downloading and rewriting of firmware can be rapidly andreliably performed.

(Redundancy of Cable)

The control system 1 having the above-described configuration can copewith the redundancy of a cable. In general, the redundancy of a cable isa configuration in which two controllers respectively connected to bothends of a control network having the plurality of slave devices 21, 22,and 23 are connected through two routes (similar configuration as thatin FIG. 1).

FIG. 23 is a diagram showing an example of a case that can be dealt withby redundancy of a cable. FIG. 23 shows a case where the communicationcable 33 connecting the slave device 22 and the slave device 23 to eachother is disconnected. In FIG. 15, a white bold arrow indicates atransmission state of a control frame.

As shown in FIG. 23, the control system 1 includes a first route and asecond route. In the first route, the plurality of slave devices 21, 22,and 23 is connected in order between the controller 11 and thecontroller 12 using the plurality of communication cables 31, 32, 33,and 34. In the second route, the controller 11 and the controller 12 aredirectly connected to each other through the communication cable 35. Ingeneral, the controller 11 transmits a control frame through the firstroute.

Here, in a case where the communication cable 33 is disconnected, thecontrol frame transmitted from the controller 11 is looped back by theslave device 22. The controller 11 confirms PDO or a time stamp of thecontrol frame. When it is detected that the control frame has not passedthrough the slave device 23, the controller 11 loops back the controlframe to the second route. The control frame reaches the slave device 23through the second route and the controller 12. When the slave device 22side is viewed from the slave device 23, the slave device 22 is notconnected, and thus the slave device 23 loops back the control frame tothe controller 12 side. The controller 12 loops back the control frameto the controller 11 through the second route.

(Specific Process of Controller in Run Mode)

The controller 11 in a run mode specifically executes the followingprocess. FIG. 24 is a flowchart of a process of the controller in a runmode corresponding to redundancy of a cable.

The controller 11 in a run mode transmits a control frame through thefirst route (a route in which the plurality of slave devices 21, 22, and23 is connected between the controller 11 and the controller 12) (S501).The controller 11 receives the control frame (S502).

The controller 11 analyzes the control frame and detects whether or notthere is a slave device through which the control frame has not passed.For example, the controller 11 detects whether or not there is a slavedevice through which the control frame has not passed, based on thepresence or absence of a time stamp in each slave device andconsistency.

When there is no slave device through which the control frame has notpassed (S503: NO), the controller 11 continues general control, that is,control for transmitting the control frame from the first route.

When there is a slave device through which the control frame has notpassed (S503: YES), the controller 11 loops back the control frame tothe second route and transfers the control frame (S504).

(Specific Process of Controller in Data Acquisition Mode)

The controller 12 in a data acquisition mode specifically executes thefollowing process. FIG. 25 is a flowchart of a process of the controllerin a data acquisition mode corresponding to redundancy of a cable.

The controller 12 in a data acquisition mode cannot receive a controlframe from the first route and receives a control frame from the secondroute (S511). The controller 12 loops back the control frame to thefirst route and transmits the control frame (S512). The controller 12receives the control frame from the first route (S513).

The controller 12 loops back the control frame to the second route andtransmits the control frame (S514).

In addition, the controller 12 transmits the control frame to thedatabase device 40 of the information communication network 60 (S511).The controller 12 extracts PDO data from the control frame (S531) andstores the extracted PDO data in the shared memory 104′ (S532).

With the above-described configuration and process, the controller 11can transmit control frames to all of the plurality of slave devices 21,22, and 23 and receive control frames updated in all of the plurality ofslave devices 21, 22, and 23 even when disconnection or the like occursin the middle of the first route. That is, even when disconnectionoccurs in the middle of the first route, the controller 11 continues thecontrol of the plurality of slave devices 21, 22, and 23. This is notdependent on the location of disconnection, and naturally, thecontroller 11 continues the control of the plurality of slave devices21, 22, and 23 even when disconnection occurs in the middle of thesecond route, that is, the communication cable 35.

(Abnormality Detection by Controller in Data Acquisition Mode)

In the above-described configuration, a mode in which an abnormalitydetection process is executed by the database device 40 connected to theinformation communication network 60 has been described. However, anabnormality detection process may be performed by the controller in adata acquisition mode.

FIG. 26 is a diagram showing a configuration of a device in a controlsystem in a case where abnormality detection is executed by a controllerin a data acquisition mode. FIG. 27 is a block diagram showing aconfiguration related to data communication in a controller in a dataacquisition mode.

A control system 1B shown in FIG. 26 is different from the controlsystem 1 shown in FIG. 1 in that a controller 11B is used instead of thecontroller 11, a controller 12B is used instead of the controller 12,and the database device 40 is not an essential component. Othercomponents of the control system 1B are the same as those of the controlsystem 1, and description of the same parts will be omitted.

The controller 11B and the controller 12B have the same configuration,and are different from the controller 11 and the controller 12 in that apacket analyzer 106 as shown in FIG. 27 is added. The controller 11B andthe controller 12B operate in different modes. For example, when thecontroller 11B is operating in the above-described run mode, thecontroller 12B is operating in the above-described data acquisitionmode.

Further, the controller 12B executes a process related to abnormalitydetection executed by the above-described database device 40 is executedby the packet analyzer 106. Since the controller 12B is operating in adata acquisition mode, control of the control network is not affectedeven when abnormality detection is performed. Therefore, the controlsystem 1B can execute abnormality detection using only a deviceconnected to the control network while reliably executing control of theplurality of slave devices 21, 22, and 23. Meanwhile, in this case, thecontroller 12B may output a result of the abnormality detection to theinformation communication network 60. For example, the controller 12Boutputs the result of the abnormality detection to the UI device 50through the information communication network 60. The UI device 50 or anoperator operating the UI device 50 determines a command and the likefor the controller 11B based on the result of the abnormality detection.

In addition, it is preferable that the packet analyzer 106 be realizedby a dedicated IC different from the CPU 101′, for example, an ASIC.Thereby, a processing load on the CPU 101′ of the controller 12B in adata acquisition mode can be reduced.

Further, in this case, it is preferable that the transception part 102′transmit a control frame to the packet analyzer 106 through DMAtransmission. Thereby, a load of the CPU 101′ is further reduced.

Meanwhile, in the configurations shown in FIGS. 26 and 27, a mode inwhich both the controller 11B and the controller 12B have the sameconfiguration has been described, but the packet analyzer 106 may beincluded in only the controller 12B.

What is claimed is:
 1. A control system comprising: a field bus to whichslave devices are linearly connected through a communication cable; afirst controller which is connected to one end of the field bus; asecond controller which is connected to the other end of the field bus;and a data communication network that connects the first controller andthe second controller without going through the slave devices, whereineach of the first controller and the second controller includes acontrol frame generation part which generates a control frame to beprovided to the slave devices, and a transception part which transmitsand receives the control frame to and from the slave devices, and one ofthe first controller and the second controller generates the controlframe by the control frame generation part, transmits the generatedcontrol frame from the transception part, and the other one performsloopback communication of the control frame by the transception part,when the first controller generates and transmits the control frame andthe second controller performs the loopback communication of the controlframe, the second controller transmits an operation confirmation signalto the first controller through the data communication network, andstarts generation and transmission of the control frame when a responsesignal to the operation confirmation signal is not able to be received.2. The control system according to claim 1, wherein the secondcontroller observes the control frame and starts generation andtransmission of the control frame when the control frame is not able tobe received over a predetermined period of time.
 3. The control systemaccording to claim 2, further comprising: a user interface device whichis connected to the data communication network and receives an operationinput of switching of control between the first controller and thesecond controller, wherein when the first controller generates andtransmits the control frame and the second controller performs loopbackcommunication of the control frame, the first controller stopsgeneration and transmission of the control frame and starts the loopbackcommunication of the control frame when receiving a command for theswitching of the control from the user interface device, and the secondcontroller stops the loopback communication of the control frame whenreceiving a command for the switching of the control from the userinterface device and starts the generation and the transmission of thecontrol frame.
 4. The control system according to claim 2, wherein thecontrol frame generation part and the transception part are formed ofdifferent semiconductor devices.
 5. The control system according toclaim 4, wherein the control frame generation part is constituted by acomputation element that executes a generation program for the controlframe, and the transception part is constituted by a semiconductorelement that exclusively performs transmission and reception of thecontrol frame.
 6. The control system according to claim 1, furthercomprising: a user interface device which is connected to the datacommunication network and receives an operation input of switching ofcontrol between the first controller and the second controller, whereinwhen the first controller generates and transmits the control frame andthe second controller performs loopback communication of the controlframe, the first controller stops generation and transmission of thecontrol frame and starts the loopback communication of the control framewhen receiving a command for the switching of the control from the userinterface device, and the second controller stops the loopbackcommunication of the control frame when receiving a command for theswitching of the control from the user interface device and starts thegeneration and the transmission of the control frame.
 7. The controlsystem according to claim 6, wherein after the first controller and thesecond controller transmit and receive a switching confirmation signaland mutually confirm the switching, the first controller stops thegeneration and the transmission of the control frame and starts theloopback communication of the control frame, and the second controllerstops the loopback communication of the control frame and starts thegeneration and the transmission of the control frame.
 8. The controlsystem according to claim 6, wherein the control fame generation partand the transception part are formed of different semiconductor devices.9. The control system according to claim 8, wherein the control framegeneration part is constituted by a computation element that executes ageneration program for the control frame, and the transception part isconstituted by a semiconductor element that exclusively performstransmission and reception of the control frame.
 10. The control systemaccording to claim 1, wherein the control frame generation part and thetransception part are formed of different semiconductor devices.
 11. Thecontrol system according to claim 10, wherein the control framegeneration part is constituted by a computation element that executes ageneration program for the control frame, and the transception part isconstituted by a semiconductor element that exclusively performstransmission and reception of the control frame.
 12. The control systemaccording to claim 7, wherein the control frame generation part and thetransception part are formed of different semiconductor devices.
 13. Thecontrol system according to claim 12, wherein the control framegeneration part is constituted by a computation element that executes ageneration program for the control frame, and the transception part isconstituted by a semiconductor element that exclusively performstransmission and reception of the control frame.
 14. A control methodcomprising: connecting a first controller to one end of a field bus towhich slave devices are linearly connected through a communicationcable; connecting a second controller to the other end of the field bus;connecting the first controller and the second controller by a datacommunication network without going through the slave devices, the firstcontroller generates a control frame that is provided to the slavedevices, and transmits the control frame to the slave devices, and thesecond controller transmits an operation confirmation signal to thefirst controller through the data communication network while performingloopback communication of the control frame, and generates and transmitsthe control frame to the slave devices when a response signal to theoperation confirmation signal is not able to be received.
 15. A controlsystem comprising: a field bus to which slave devices are linearlyconnected through a communication cable; a first controller which isconnected to one end of the field bus; a second controller which isconnected to the other end of the field bus; a data communicationnetwork that connects the first controller and the second controllerwithout going through the slave devices; and a user interface devicewhich is connected to the data communication network and receives anoperation input of switching of control between the first controller andthe second controller, wherein each of the first controller and thesecond controller includes a control frame generation part whichgenerates a control frame to be provided to the slave devices, and atransception part which transmits and receives the control frame to andfrom the slave devices, and one of the first controller and the secondcontroller generates the control frame by the control frame generationpart, transmits the generated control frame from the transception part,and the other one performs loopback communication of the control frameby the transception part, and when the first controller generates andtransmits the control frame and the second controller performs loopbackcommunication of the control frame, the first controller stopsgeneration and transmission of the control frame and starts the loopbackcommunication of the control frame when receiving a command for theswitching of the control from the user interface device, and the secondcontroller stops the loopback communication of the control frame andstarts the generation and the transmission of the control frame whenreceiving a command for the switching of the control from the userinterface device.